The present invention relates generally to activated carbon and a method of forming the same and, more particularly, to a method of producing highly porous adsorbents using thermal oxygen activation.
Activated carbon is commonly used to remove pollutants, contaminants, and other impurities from gaseous and liquid media, including air and water. It is used in a wide variety of applications throughout a broad range of industries. Activated carbon is a highly porous and adsorptive material comprised primarily of carbon atoms. A network of connected micro- and mesopores trap contaminants, pollutants, and other impurities that enter the material by the process of adsorption, in which atoms, ions, and molecules adsorb or attach to the surface of the carbonaceous material. The effectiveness of activated carbon is generally improved with increased micro- and/or mesopore surface area and by finely tuning pore size to match the size of contaminants of concern. Pores significantly larger than the contaminants of concern are generally ineffective in trapping the contaminants.
Activated carbons have been manufactured from a wide variety of biomass materials, including coconut shells, wood, peat, among many other materials, as well as fossilized plant material (e.g., lignite and bituminous coal). Existing technologies for producing activated carbons include physical activation and chemical activation. Physical activation methods use carbon dioxide or steam as the activating gas at a relatively high temperature (e.g., >700° C.) in specially designed reactors. Chemical activation is typically conducted in the presence of nitrogen at a lower temperature and requires the addition of reactive chemical agents, such as zinc chloride or phosphoric acid.
Little research is available on thermal oxygen activation and that which has been conducted has included the addition of other gases (e.g., nitrogen or helium) to the air to serve as thermal ballast. Experiments conducted by Dai et al. with pure air showed some burning, evidenced by ash formation. Dai et al. (Dai et al., “High Yield Activated Carbon from Biomass by Air Activation,” 864) concluded the necessity to control temperature and oxygen partial pressure was one of the reasons activated carbon was difficult to produce by air/oxygen activation.